Process of treating magnetic material



Patented Nov. 8, 1927.

UNITED STATES- PATENT OFFICE.

WILLIAM E. RUDER, 0F SCHENECTADY, NEW YORK, ASSIGNOR TO GENERAL ELECTRIC I COMPANY, A CORPORATION OF NEW YORK.

PROCESS OF TREATING MAGNETIC MATERIAL.

N'o Drawing.

The present invention relatesto magnetic steel such as used, for example, in the manufacture of transformer cores, dynamo-electric machinery and the like, and my invention comprises a method of treating steel sheets toimprove their magnetic properties, and an improved product resulting from this method.

I have discovered that when sheets of magnetic steel are treated so as to remove a surface layer upon the sheets, as by pickl ng in acid, in conjunction with an annealing treatment under deoxidizing or purifying conditions, as in a vacuum, or in a reducing but not carburizi-ng gas, regardless of the order in which these steps are carried out, the magnetic permeability is increased and the energy loss during operation is decreased. By the expression not carburizing I mean a gas which will not give up carbon. to the sheet steel material which is subjected to the action of the gas.

Alloy steel, of which steel containing about three to five per cent of silicon is a conspicuous example, is prepared for use by rolling ingots of steel into sheet form by methods which are well known. Apparently a surface skin of the metal is modified by the rollin 'process so as to be less Susceptible to a subsequent annealing treatment whereby the magnetic properties of the sheets are improved. Whether it is a fact or -not that such a surface layer exists (other than the usual surface scale) is diflicult todemonstrate by tests other than the undoubted improvement of magnetic properties of the sheets due to its removal in accordance with my invention. Y

Prior to my invention pickling of silicon steel has been practised with some beneficial effect which was due to the removalof a use less surface scale of oxide. Its removal resulted in a better space factor inthe.fin-' ished apparatus, but no substantial improvement of the steel itself're'sulted. My experiments indicate that when the pickling was followed by an anneal in contact with gases such as carbon monoxide, this gas undid whatever benefit had been obtained by pick- :ling. Even when closed annealing pots were used, carbon monoxide was in contact with the steel.,.,.. It now appears that the pickling treatment'fleft the steel in a conditionpeculiarly susceptible to gases which are present Application filed January 23, 1924. Serial No. 688,090.

in ordinary annealing furnaces, and that these gases had a deleterious effect.

\Vhen carrying out the process constitut ing my invention the annealing treatment which either precedes picklmg or follows pickling, is carried out under conditions 'WhlCll Wlll not permit of the absorption of to the usual finishing step s'such as galvanizin'g, japanning, or enameling. For example, the sheets may be immersed in an aqueous solution containing about ten to twenty per cent sulphuric acid. Solutions of hydrochloric or other acids also may be used. The pickling is continued until the scale on the sheets is completely removed. This scale is formed during rolling and usually is thin but is closely adherent. During the removal of the scale from all parts of the surface, a thin layer of the underlying metal also is removed. Usually about fifteen minutes is a suflicient length of time for pickling, but some conditions may require a longer time. The sheets then are washed, dried and annealed in a vacuum or in hydrogen as at about 800 to 850 degrees centrigra e for about one hour. The annealing process may be carried out in a furnace such as described 'in my prior Patent No. 1,110,010 of Septem- .netic flux and the hysteresis watt losses'are' decreased. about ten to fifteen-per cent, de-, pending on the condition of the steel.

prior to pickling, preferably after all the mechanical work such as rolling and unching has been'done on the sheets. referably, the process described inmy prior Ila ent No. 1,110,010 is employed for the anneal, although the annealing-temperature need not necessarily be any higher that 800 to 850 de- -1o0 In some cases the steel maybe annealed j loss are even reater than when the anneal P grees centigrade. After anneal the sheets are pickled as above described. In this case,

the improvements in permeability and watt follows pickling. Permeability at working .density is increased about fifteen per centi and the watt loss is decreased about twenty per cent as compared with the same steel treated by methods previously used involv ing pickling followed by an anneal which did not remove gases of a harmful nature, which are present in the steel or prevent access of deleterious gases to the steel sheets during anneal.

-VVhat I claim as new and desire to secure by Letters Patent of the United States, is:

r ubstantially non-oxygenous condition therem. V v

2. The method of treating silicon steel sheets which consists in pickling said sheets in an acid bath to remove a surface skin, and

annealing said sheets under conditions favorable to the removal of deleterious gases.

3. The method of treating silicon steel sheets which consists in removing a surface film from said sheets and annealing said sheets under reducing but not carburizing conditions.

4. The method of treating rolled silicon steel sheets which consists in pickling said sheets in an acid bath to remove a surface film and annealing said sheets under reducing but not carburizing conditions.

5. The method vof treating rolled silicon steel sheets which consists in pickling said sheets in dilute acid until a surface film has been removed and annealing said sheets in the presence of hydrogen at about 800 to 850 degrees centigrade.

6. The method of improving the magnetic properties of alloy steel sheets which comprises pickling the sheets to remove a surface film and annealing the sheets under reducing but not carburizing conditions.

7. The method of improving the magnetic properties of alloy steel sheets which comprises removing a surface layer from said sheets and annealing the sheets under conditions favorable to the removal of deleterious gases. a

In witness whereof, I have hereunto set my hand this 22nd'day of J anuary,-1924.

* WILLIAM E. RUDER. 

